System and method for fault handling in a propulsion system for an electric vehicle

ABSTRACT

A propulsion system for an electric vehicle comprising a high voltage battery unit having a first high voltage battery connected in series with a second high voltage battery, which may also be referred to as a first and second battery bank, and one or more power inverters arranged to connect the battery banks to one or more electric machines. The one or more power inverters and the one or more electric machines are configured to form a first and a second three-phase system, and the system and method relates to fault handling if a fault is detected in one of the first and second three-phase system. The architecture incorporating dual battery banks, and dual and/or multiphase inverters and electric machines can provide enhanced redundancy and limp home functionality in cases where a fault or error occurs in the inverter and/or in the electric machine so that a faulty three-phase system can be operated in a safe pulse-off mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure claims the benefit of priority co-pendingEuropean Patent Application No. 19173027.4, filed on May 7, 2019, andentitled “SYSTEM AND METHOD FOR FAULT HANDING IN A PROPULSION SYSTEM FORAN ELECTRIC VEHICLE,” the contents of which are incorporated in full byreference herein. The presence disclosure also incorporates EuropeanPatent Application Nos. 19173020.9 and 19173040.7 in full by referenceherein.

TECHNICAL FIELD

The present disclosure relates to systems and methods for fault handlingin a propulsion system for an electric vehicle.

BACKGROUND

Electric vehicles generally relate to vehicles that have batteries orbattery units that store energy, where the batteries are designed toprovide electric power for propelling and accelerating the vehicle andalso for providing power to electric systems used in the vehicle. Thestored energy is consumed when the electric vehicle is driven, and thebattery needs to be re-charged to replenish the level of stored energythrough a connection to an external electric power supply.

Due to the existing charging infrastructure with charging stationshaving different properties, it has been found that it is advantageousto be able to charge the vehicle using different charging voltages, suchas 400V and 800V. Moreover, propulsion systems exist for operation ateither 400V or 800V. In view of the above, there is an ongoingdevelopment of propulsion systems for electric vehicles which arecapable of receiving both a 400V and an 800V charging voltage.

In a propulsion system for an electric vehicle, errors and faults suchas sensor failures in the electric machine or in the inverter must behandled in such a way that the vehicle can still be operated even if thefunctionality and performance is reduced, for example in a so calledlimp home mode, until the driver can take the vehicle to a safe locationor to a workshop. Furthermore, if the vehicle speed is high when a faultoccurs it is important that the failed system can be maintained in asafe state long enough for the vehicle speed to be reduced to levels lowenough to be able to exit the safe state mode and drive the vehicle fora longer time in a limp home mode, or for the driver to safely be ableto drive the vehicle to a workshop.

In view of the above, there is an ongoing development of propulsionsystems for electric vehicles which are capable of receiving both a 400Vand an 800V charging voltage. However, the development of propulsionsystems architectures incorporating capable of handling both 400V and800V comes with challenges but also provides new opportunities for howto implement the required fault handling functionalities.

Accordingly, there is room for further improvement of fault handling inpropulsion systems for electric vehicles that allow for safe-state andlimp home operation.

SUMMARY

In general, the disclosed subject matter relates to a propulsion systemfor an electric vehicle and to fault handling in a dual battery bankpropulsion system. The system comprises a high voltage battery unitcomprising a first high voltage battery connected in series with asecond high voltage battery, which may also be referred to as a firstand second battery bank, and one or more power inverters arranged toconnect the battery banks to one or more electric machines. The one ormore power inverters and the one or more electric machines areconfigured to form a first and a second three-phase system, and thesystem and method relates to fault handling if a fault is detected inone of the first and second three-phase system.

The invention is based on the realization that an architectureincorporating dual battery banks, and dual and/or multiphase invertersand electric machines can provide enhanced redundancy and limp homefunctionality in cases where a fault or error occurs in the inverterand/or in the electric machine so that a faulty three-phase system canbe operated in a safe state mode. One safe state mode which ispreferably used when a fault or error occur in the inverter and/or inthe electric machine is a so called safe pulse-off mode.

Safe pulse-off is a safe state where the inverter transistors are leftin an open state, switching of the transistors is stopped and thevoltage, current and phase angle to the electric machine is no longercontrolled. The safe pulse-off mode can be used as long as the back-EMF(back electromotive force) in the electric machine is lower than thecorresponding DC-voltage of the high-voltage battery unit. The relationbetween the AC back-EMF voltage and the DC-voltage includes the voltagedrop which occurs when power is transferred from DC to AC and vice versain the inverter. The amplitude of the voltage drop varies depending onthe modulation technique used in the inverter.

The back-EMF of the electric machine, sometimes referred to as thecounter-electromotive force, is the power of the magnetic flux constantand the rotational speed of the Electric Machine, which in turn isproportional to the vehicle speed. As long as the corresponding DCvoltage is not exceeded by the back-EMF no current will be charged backto the high voltage battery and thus there is no risk for overchargingor battery contactor opening. However, in cases where the back-EMF ishigher than a corresponding DC voltage, the current will flow towardsthe DC link through the anti-parallel diodes and charge the battery inan uncontrolled manner. Accordingly, the safe pulse-off mode can be usedwithout any current being back-fed into the DC circuit up to a certainrotation speed of the electric machine.

The described propulsion system further comprises a propulsion systemcontrol unit configured to detect a fault in the first or the secondthree-phase system, wherein the inverter of the three-phase systemcomprising the phase where the fault was detected is configured tooperate in a safe pulse-off mode if the back-EMF of the faultythree-phase system is lower than the corresponding DC operating voltageof the high voltage battery unit.

Accordingly, by means of the described system architecture comprisingdual battery banks, safe pulse-off can be performed at a higher vehiclespeed compared to in a single bank battery system, since the back-EMFmay be as high as the combined voltage of the first and second highvoltage batteries, i.e. as high as the nominal operating voltage of thehigh-voltage battery unit comprising the first and second high-voltagebattery arranged in series. According to an example embodiment, therespective operating voltage of the first and second high voltagebattery may be 400V meaning that safe pulse-off can be performed for aback-EMF up to 800V which is then the nominal operating voltage of thehigh-voltage battery unit.

Further features of, and advantages with, embodiments of the presentdisclosure will become apparent when studying the appended claims andthe following description. The skilled person realize that differentfeatures of the present invention may be combined to create embodimentsother than those described in the following, without departing from thescope of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates a propulsion system according to anembodiment of the invention;

FIG. 2 schematically illustrates a propulsion system according to anembodiment of the invention;

FIG. 3 schematically illustrates a propulsion system according to anembodiment of the invention;

FIG. 4 schematically illustrates a propulsion system according to anembodiment of the invention;

FIG. 5 schematically illustrates a propulsion system according to anembodiment of the invention; and

FIG. 6 is a flow chart schematically outlining steps of a method ofcontrolling a propulsion system according to embodiments of theinvention.

DESCRIPTION OF EMBODIMENTS

In the present detailed description, various embodiments of a propulsionsystem and a method for controlling the propulsion system according tothe present invention are described. However, this invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided for thoroughness and completeness, and to fully convey thescope of the invention to the skilled person. Like reference charactersrefer to like elements throughout.

FIG. 1 schematically illustrates a propulsion system 100 according to anembodiment of the invention. The propulsion system 100 comprises a highvoltage battery unit 102 having a first high voltage battery 103connected in series with a second high voltage battery 104 such that anominal operating voltage of the high voltage battery unit 102 is thesum of a voltage of the first high voltage battery 103 and a voltage ofthe second high voltage battery 104. The first and second high voltagebatteries 103, 104 may also be referred to as battery banks 103, 104.

The system 100 illustrated in FIG. 1 further comprises a firstthree-phase power inverter 105 connected to a first set 204 of threephases of a dual winding three-phase electric machine 202 and a secondthree-phase power inverter 106 connected to a second set 206 of threephases of the dual winding three-phase electric machine 202. The firstthree-phase system is here formed by the first three-phase powerinverter 105 and the first set 204 of three phases of the dual windingthree-phase electric machine 202 and the second three-phase system isformed by the second three-phase power inverter 106 and the second set206 of three phases of the dual winding three-phase electric machine202.

The system further comprises a propulsion system control unit (notshown) configured to detect a fault in the first or the secondthree-phase system, wherein the inverter of the three-phase systemcomprising the phase where the fault was detected is configured tooperate in a safe pulse-off mode, if a back electromotive force,back-EMF, of the faulty three-phase system is lower than the operatingvoltage of the high voltage battery unit 102. In the safe pulse-offmode, transistors of the power inverter in the faulty three-phase systemare maintained in an open state and switching of the transistors isstopped. It can be assumed that the inverter transistors can be left inan open state and that switching of the transistors can be stopped formost failures of the three-phase system. Examples of failures includeresolver failure in the electric machine, current sensor failure in theinverter, and temperature sensor failure in the inverter or in theelectric machine. The one of the first and second three-phase systemwhere a fault has been detected will be referred to as the faultythree-phase system and the other three-phase system will be referred toas the non-faulty three-phase system. Accordingly, even if a fault isdetected in e.g. a phase of the electric machine, the entire three-phasesystem comprising the faulty phase will be treated as being faulty.

In the following examples, a nominal operating voltage of the first andsecond high voltage battery 103, 104 is taken to be 400V. This meansthat an actual operating voltage may be somewhat above or below thenominal operating voltage at any given point in time depending on e.g.the state of charge of the battery and other operating conditions.Accordingly, a nominal operating voltage of the high voltage batteryunit 102 is here 800V.

Since the back-EMF, which is defined as a voltage, is directlyproportional to the rotational speed of the electric machine, which inturn is proportional to the vehicle speed, a higher allowed back-EMFmeans that the safe pulse-off mode may be entered at a higher vehiclespeed. Moreover, as a result of the redundancy provided by the describedpropulsion system 100 comprising a first and a second three-phasesystem, the vehicle can enter into a so called limp home mode where itis being operated by the non-fault three-phase system.

The maximum amplitude of the back-EMF is dictated by the properties ofthe electric machines used, an in particular by the power of theelectric machines. According to various embodiments of the invention,the systems can be designed so that a faulty sub-system, i.e. the firstor second three-phase system, of the propulsion system can be operatedin a safe pulse-off mode for the entire allowable range of vehiclespeeds. In operation, the back-EMF can be determined as the product ofthe speed and the magnetic flux constant of the of the electric machine,where the speed of the electric machine can be determined by measuringthe rotor position.

Depending on the system configuration used, the transistor components inthe one or more power inverters used may be dimensioned to withstandvoltage transient levels occurring when switching up to the highest DCbus voltage, in this example up to 800V. This to allow a current fromthe non-faulty three-phase system to flow from the electric machine 202through the non-faulty inverter and to the high voltage battery unit 102and vice versa depending on if the electric machine 202 is operated ingenerator mode or in motor mode. Accordingly, each of the one or morepower inverters is configured to operate at a voltage corresponding to anominal operating voltage of the high voltage battery unit 102. Duringnormal operation (i.e. when both three-phase systems are non-faulty)there will be voltage transients during switching which are above theoperating DC voltage level. Accordingly, inverter transistors rated for1200V are preferably used for 800V applications. The transients willappear in both peak torque and in a field-weakening speed region. Duringsafe pulse-off mode operation there will be no switching transients ofthe faulty three-phase system since it has been stopped from switchingwhile the normally operating 3-phase system will experience transientsas usual.

According to example embodiments of the invention, the non-faultythree-phase system is configured to provide vehicle propulsion and/orregenerative braking in a limp-home mode of the vehicle. Thereby, thelimp-home functionality is improved since the non-faulty three-phasesystem, here a 400V system, can be still be used to operate the vehicle.

The propulsion system may also be operated in an active short-circuitmode which may be achieved by leaving the lower inverter transistors ineach phase leg in an on-state, switching is stopped and current andvoltage is circulating between the phases of the inverter phases and thephases of the electric machine in a closed shorted circuited loop. Theactive short-circuit mode can thereby be used also for a back-EMF whichis higher than the corresponding DC-voltage of the high-voltage battery.However, this also means that the components of the inverter and of theelectric machine must be able to manage the active short-circuit currentlevels for the amount of time that this safe state mode is engaged.Moreover, a brake torque occurs as a result of the magnetic circuit inthe electric machine. This brake torque may influence the safety of thevehicle and must therefore not exceed a certain brake torque thresholdlevel to avoid excessive and unsafe speed retardation. Accordingly, itis preferable to operate the propulsion system in a safe pulse-off mode.

The propulsion system control unit may be a separate control unit, orthe functionality of the propulsion system control unit may be providedby several different control units. Each power inverter may for examplecomprise a control unit capable of detecting a fault in either of thedescribed three-phase systems, and to control the propulsion system tooperate in a safe pulse-off mode as described above.

Moreover, the control unit may include a microprocessor,microcontroller, programmable digital signal processor or anotherprogrammable device. The control unit may also, or instead, include anapplication specific integrated circuit, a programmable gate array orprogrammable array logic, a programmable logic device, or a digitalsignal processor. Where the control unit includes a programmable devicesuch as the microprocessor, microcontroller or programmable digitalsignal processor mentioned above, the processor may further includecomputer executable code that controls operation of the programmabledevice. The control unit may for example be a general-purpose ECU(electric control unit), or one or more application specific controlunits.

The claimed methods for controlling the vehicle propulsion system canthereby be performed by control units of the various describedcomponents, for example under control of a coordinating propulsionsystem control unit or by one or more generic vehicle ECUs (electroniccontrol units).

According to an example embodiment of the invention, the propulsionsystem control unit is configured to control the non-faulty three-phasesystem of the first and second three-phase system to provide fieldweakening current control to reduce the magnetic field in the faultythree-phase system. Field weakening is achieved by controlling theD-axis and Q-axis current in the Electric Machine. The current controlis for example done by the motor core software in the power inverter.The D-axis current is increased in a negative direction to decrease themagnetic flux in the machine (thus called field weakening). The positiveQ-axis current is simultaneously decreased. By using field weakening inthe non-faulty system, the short-circuit current and braking torque ofthe faulty system is reduced which in turn reduces the back-EMF andthereby allows the propulsion system to use the safe pulse-off mode at ahigher vehicle speed compared to if no field weakening is used, meaningthat it may be possible to avoid using the active short-circuit mode.

The illustrated propulsion system further 100 comprises a plurality ofloads 110, 112, 114 which are here arranged to be powered the first highvoltage battery 103. It should be noted that the loads equally well maybe powered by the second high voltage battery 104. By connecting theloads to one of the 400V battery banks 103, 104, conventional 400Vcomponents may be used also in an 800V propulsion system in order tomaximize the features in common with a 400V system, thereby reducing thecost and complexity of the 800V system 100, and in particular tofacilitate the transition from 400V to 800V system architectures. Theloads 110, 112, 114 may for example be components operating at 400V suchat heaters, climate control systems or the like, or the loads may beDC/DC converters down-converting the 400V voltage for providing power toa 48V system and/or to a 12V system.

Moreover, the system 100 comprises a switch 116 connected to aDC-charging inlet 117, the switch 116 being configured to connect theDC-charging inlet 117 to the first high voltage battery 103 or to thehigh voltage battery unit 102 based on an amplitude of a receivedvoltage from the DC-charging inlet 117. Thereby, the vehicle may becharged by an external charging unit using either a 400V or an 800Vinput voltage.

FIG. 2 schematically illustrates a propulsion system 200 according to anexample embodiment of the invention. The system comprises a six-phasepower inverter 302 connected to a six-phase electric machine 304,wherein the first three-phase system is formed by a first set of threephases 306 of the six-phase power inverter 302 and a corresponding firstset of three phases 306 of the six-phase electric machine 304 and thesecond three-phase system is formed by a second set of three phases 308of the six-phase power inverter 302 and a corresponding second set ofthree phases 308 of the six-phase electric machine 304.

The six-phase power inverter 302 is configured to provide two differentvoltages, e.g. 400V and 800V, in order to be able to charge both of thefirst and second high voltage batteries 103, 104 as well as ahigh-voltage battery unit 102. The operation of the system of FIG. 2 issimilar to what is described above with reference to the systemillustrated by FIG. 1. A power inverter 302 configured to operate at800V may preferably be rated at 1200V, meaning that it is capable ofhandling a higher back-EMF compared to a 400V inverter which may berated at e.g. 700V.

FIG. 3 schematically illustrates a propulsion system 300 according to anexample embodiment of the invention. The propulsion system 300 comprisesa first three-phase inverter 105 connected to a first set 406 of threephases of a six-phase electric machine 402 and a second three-phaseinverter 106 connected to a second set 408 of three phases of thesix-phase electric machine 402, wherein the first three-phase system isformed by the first three-phase power inverter 105 and of a first set ofthree phases 406 of the six-phase electric machine 402 and the secondthree-phase system is formed by the second three-phase power inverter106 and a second set of three phases 408 of the six-phase electricmachine 402. The operation of the system of FIG. 3 is similar to what isdescribed above with reference to the systems illustrated by FIGS. 1-2.

FIG. 4 schematically illustrates a propulsion system 400 according to anexample embodiment of the invention. The propulsion system 400 comprisesa multilevel power inverter 502 connected to an electric machine 504,wherein the propulsion system control unit is configured to detect afault in a level of the multilevel inverter 504 and to control anon-faulty level of the multilevel inverter 504 to provide vehiclepropulsion and/or regenerative braking. The multilevel inverter 502 maybe a six-phase power-inverter and the electric machine a correspondingthree-phase or six-phase electric machine. A fault in a level of themultilevel inverter 502 means a fault in between two of the levels inthe inverter. The multilevel inverter 502 in FIG. 4 may have 3 levels.0V, 400V and 800 V. Half of the modules of the inverter 502 containtransistors and diodes operating between 0V and 400 V and half of thembetween 400V and 800V. If a fault occurs in the modules working between0-400V connected to the first battery bank, the other modules workingbetween 400 and 800V connected to the second battery bank can stilloperate the vehicle but with decreased performance compared to when allmodules are operating, e.g. in a limp-home mode. Further operation ofthe system of FIG. 4 is similar to what is described above withreference to the systems illustrated by FIGS. 1-3.

FIG. 5 schematically illustrates a propulsion system 500 according to anexample embodiment of the invention. The propulsion system 500 comprisesan electric machine 602 having three windings 604 coupled to athree-phase AC charging inlet 606, wherein the propulsion system controlunit is configured to charge the first and/or the second high voltagebattery 103, 104 via the non-faulty three-phase system of the first andthe second three-phase systems. Thereby, charging may continue even if afault is detected in a phase of the electric machine 602 or in either ofthe first and second power inverters 608, 610, thereby providingenhanced redundancy for charging.

FIG. 6 is a flow chart outlining general steps of a method according toembodiments of the invention. The method comprises detecting S1, by apropulsion system control unit, a fault in the first or the secondthree-phase system. The fault may for example be detected by an inverterin the propulsion system.

Next, the method comprises determining if S2 a back electromotive force,back-EMF, of the faulty three-phase system is lower than the operatingvoltage V_(BU) of the high-voltage battery unit 202. If the back-EMF islower than or equal to the operating voltage V_(BU) of the high-voltagebattery unit 202, the method comprises operating S3 the inverter of thethree-phase system comprising the phase where the fault was detected ina safe pulse-off mode by controlling the transistors of the inverter tobe in an open state and stopping switching of the transistors. The stepof determining if S2 the back-EMF of the faulty three-phase system islower or higher than the battery voltage can for example be performed bycomparing a measured back-EMF with a measured battery voltage. Thereby,as long as the corresponding DC operating voltage V_(BU) is not exceededby the back-EMF, no current will flow back to the high voltage batteryunit 202 and thus there is no risk for overcharging the first and secondhigh voltage batteries 103, 104.

The described method can be performed by the propulsion systemsillustrated in FIGS. 1-4 and described above.

Even though the invention has been described with reference to specificexemplifying embodiments thereof, many different alterations,modifications and the like will become apparent for those skilled in theart. Also, it should be noted that parts of the system may be omitted,interchanged or arranged in various ways, the system yet being able toperform the functionality of the present invention.

Additionally, variations to the disclosed embodiments can be understoodand effected by the skilled person in practicing the claimed invention,from a study of the drawings, the disclosure, and the appended claims.In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

What is claimed is:
 1. A propulsion system for an electric vehicle, thesystem comprising: a high voltage battery unit having a first highvoltage battery connected in series with a second high voltage batterysuch that a nominal operating voltage of the high voltage battery unitis the sum of a voltage of the first high voltage battery and a voltageof the second high voltage battery; one or more power inverters arrangedto connect the high voltage battery unit and the first high voltagebattery to one or more electric machines, wherein the one or more powerinverters and the one or more electric machines are configured to form afirst and a second three-phase system; and a propulsion system controlunit configured to detect a fault in the first or the second three-phasesystem, wherein the power inverter of the faulty three-phase system isconfigured to operate in a safe pulse-off mode, where transistors of thepower inverter are in an open state and switching of the transistors isstopped, if a back electromotive force, back-EMF, of the faultythree-phase system is lower than the operating voltage of the highvoltage battery unit.
 2. The propulsion system according to claim 1,wherein the propulsion system control unit is configured to control thenon-faulty three-phase system of the first and second three-phase systemto provide field weakening current control to reduce the magnetic fieldin the faulty three-phase system.
 3. The propulsion system according toclaim 1, wherein each of the one or more power inverters is configuredto operate at a voltage corresponding to a nominal operating voltage ofthe high voltage battery unit.
 4. The propulsion system according toclaim 1, wherein the non-faulty three-phase system is configured toprovide vehicle propulsion and/or regenerative braking.
 5. Thepropulsion system according to claim 1, comprising a first powerinverter connected to a first set of three phases of a dual windingthree-phase electric machine and a second power inverter connected to asecond set of three phases of the dual winding three-phase electricmachine, wherein the first three-phase system is formed by the firstpower inverter and the first set of three phases of the dual windingthree-phase electric machine and the second three-phase system is formedby the second power inverter and the second set of three phases of thedual winding three-phase electric machine.
 6. The propulsion systemaccording to claim 1, comprising a six-phase power inverter connected toa six-phase electric machine, wherein the first three-phase system isformed by a first set of three phases of the six-phase power inverterand a corresponding first set of three phases of the six-phase electricmachine and the second three-phase system is formed by a second set ofthree phases of the six-phase power inverter and a corresponding secondset of three phases of the six-phase electric machine.
 7. The propulsionsystem according to claim 1, comprising a first three-phase powerinverter connected to a first set of three phases of a six-phaseelectric machine and a second three-phase power inverter connected to asecond set of three phases of the six-phase electric machine, whereinthe first three-phase system is formed by a first three-phase powerinverter and of a first set of three phases of the six-phase electricmachine and the second three-phase system is formed by a secondthree-phase power inverter and a second set of three phases of thesix-phase electric machine.
 8. The propulsion system according to claim1, comprising a multilevel power inverter connected to an electricmachine, wherein the propulsion system control unit is configured todetect a fault in a level of the multilevel power inverter and tocontrol a non-faulty level of the multilevel inverter to provide vehiclepropulsion and/or regenerative braking.
 9. The propulsion systemaccording to claim 1, comprising an electric machine having threewindings coupled to a three-phase AC charging inlet, wherein thepropulsion system control unit is configured to charge the first and/orthe second high voltage battery via the non-faulty three-phase system ofthe first and the second three-phase systems.
 10. A vehicle comprising apropulsion system according to claim
 1. 11. A method for controlling apropulsion system for an electric vehicle having a high voltage batteryunit having a first high voltage battery connected in series with asecond high voltage battery such that a nominal operating voltage of thehigh voltage battery unit is the sum of a voltage of the first highvoltage battery and a voltage of the second high voltage battery and oneor more power inverters arranged to connect the high voltage batteryunit and the first high voltage battery to one or more electricmachines, wherein the one or more power inverters and the one or moreelectric machines are configured to form a first and a secondthree-phase system; the method comprising: detecting, by a propulsionsystem control unit, a fault in the first or the second three-phasesystem; and if a back electromotive force, back-EMF, of the faultythree-phase system is lower than the operating voltage of the highvoltage battery unit, operating the inverter of the three-phase systemcomprising the phase where the fault was detected in a safe pulse-offmode by controlling the transistors of the inverter to be in an openstate and stopping switching of the transistors.
 12. The methodaccording to claim 11, further comprising controlling the non-faultythree-phase system of the first and second three-phase system to providefield weakening current control to reduce the magnetic field in thefaulty three-phase system.
 13. The method according to claim 11, furthercomprising controlling the power inverter of the non-faulty three-phasesystem to operate at a voltage higher than a nominal operating voltageof the non-faulty three-phase system during a transition period.
 14. Themethod according to claim 11, further comprising controlling thenon-faulty three-phase system to provide vehicle propulsion and/orregenerative braking.
 15. The method according to claim 11, in a systemhaving an electric machine having three windings coupled to athree-phase AC charging inlet, further comprising controlling thenon-faulty three-phase system to charge the first and/or the second highvoltage battery.